This application is based on Application No. 2001-343143, filed in Japan on Nov. 8, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
This invention relates to a motor network control system for controlling a plurality of inverter built-in motors through network communications.
2. Description of the Related Art
FIG. 7 shows the schematic construction of such a kind of known motor network control system. In FIG. 7, the network control system as illustrated includes a power supply 1, a network control computer 2, a plurality of motor units 3a-3c, power cables 7 and a communication cable 8. Each of the motor units 3a-3c has a motor 4, a control inverter 5 and a communication part 6.
The network control computer 2 supplies control commands for performing control by the inverters 5 to the communication parts 6 of the respective motor units 3a-3c through the communication cable 8. In addition, the power supply 1 supplies electric power to the inverters 5 of the respective motor units 3a-3c through the power cables 7, respectively. The communication cable 8 is extended from the network control computer 2 so as to connect the communication parts 6 of the respective motor units 3a-3c in series with each other. On the other hand, the power cables 7 are individually connected from the power supply 1 to the inverters 5 of the respective motor units 3a-3c. 
In the known motor network control system as constructed above, the power cables are individually connected from the power supply to the respective motor units, and hence in a system where the distance between the power supply and each motor unit becomes longer than the distances between the motor units for instance, the total wiring length of the power cables becomes long in comparison with the communication cable which connects the communication parts of the respective motor units in series with each other. As a result, the advantages such as the easiness in wiring operation and the reduction in the wiring length due to the series connection of the communication parts through the communication cable could not be made available to any satisfactory extent.
Moreover, in cases where the motor units are respectively arranged at locations away from one another, the number of power cables required for connecting between the power supply and the respective motor units becomes greater than that of the communication cable, and the total cable run length of the power cables increases as compared with the communication cable. As a consequence, the wiring operation becomes difficult upon installation.
The reason for not wiring the power cables to connect the inverters of the respective motor units in series with each other like the communication cable is as follows. That is, in the event that there takes place a failure in one of the plurality of motor units, requiring the replacement of the failed motor or inverter, if a power cable is arranged to connect the inverters of the respective motor units in series with each other, it is necessary to stop the supply of electric power to the normally operating motor units other than the failed one in order to carry out the replacement operation, and hence it is forced to even shut down the motor units unrelated to the failure and replacement.
The present invention is intended to obviate the various problems as referred to above, and has for its object to provide a motor network control system which is capable of reducing the wiring length of a power cable, making it easy to carry out a wiring operation, and preventing adverse influences on failure-unrelated normal motor units upon replacement of a failed motor or inverter.
Bearing the above object in mind, the present invention resides in a motor network control system comprising: a plurality of motor units each including a motor, an inverter for controlling the motor, and a communication part which receives a control command from an external network control computer connected therewith through a network and supplies the control command thus received to the inverter; a communication cable connecting between the network control computer and the communication part of each of the motor units; and a power cable extending successively from a power supply to the inverters of the respective motor units for sequentially connecting the power supply with the inverters in a cascade fashion from a preceding inverter at a power supply side to a following inverter.
In a preferred form of the present invention, the communication cable extends successively from the network control computer to the respective communication parts of the motor units to connect the communication parts with each other in a cascade fashion from a preceding communication part to a following communication part.
In another preferred form of the present invention, each of the motor units includes a connection board on which an associated one of the inverters and an associated one of the communication parts are installed, and which is detachably mounted on an associated one of the motors in such a manner that electric connection of the associated inverter and the associated communication part with the associated motor can be broken or made.
In a further preferred form of the present invention, the power cable and the communication cable are connected with the inverters or the communication parts through connection terminal blocks, respectively, and each of the connection terminal blocks includes a cable connector for electrically connecting the cables extending from a preceding motor unit and the cables extending to a following motor unit with each other, and a terminal block fixture for detachably fixing the cable connector to an inverter side or a communication part side.
In a still further preferred form of the present invention, the motor network control system further comprises a reactor inserted in the power cable in each of the motor units.
The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings.